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State investigators and personnel from Great America are dismantling the Invertigo roller coaster as part of the effort to determine what caused a malfunction that left 24 riders stranded in mid-air for more than four hours last month.

Erika Monterroza, a spokeswoman for the California Division of Occupational Safety and Health, said today she did not know exactly when the dismantling began. No information will be released until the investigation is concluded, she said.

Roller Coaster Riders Stuck in Heat at Great America

Preliminary reports indicate that on Aug. 10, the lift chain that pulls riders up the tracks on the roller coaster's 138-foot lift malfunctioned. The people on the lower end were at least 40 feet off the ground, with the people on top another 40 feet or so higher.

Urban search and rescue crews from San Jose, Santa Clara and Santa Clara County fire departments conducted a four-hour rescue operation to release 24 riders from their protective harnesses and return them safely to the ground.

Cal-OSHA's elevator, ride and tramway unit is dismantling the ride as part of its follow-up investigation, according to Monterroza. Investigators may send specific parts away for analysis, she said.

The investigation also involves interviewing riders and staff and examining maintenance records for the ride, she said. It's not yet clear when the investigation will be complete.

Many of those stuck on the ride could be seen swinging their legs back and forth as they waited to be rescued.

Invertigo is North America's first inverted face-to-face roller coaster. It consists of seven-car train that takes riders upside down six times, to heights of up to 161 feet, in one minute and 10 seconds, according to Great America's Web site.

The Invertigo incident was not the first time emergency crews have been called to the park:

In 1980, a teenager was killed on a roller coaster called The Wizzer.

In 1989 a boy died after jumping from the loggers-run flume-ride.

In 1998, a man died after he climbed a fence to retrieve a hat, lost under the Top Gun coaster.